Certain data, once received, should not be subsequently altered or modified, because of the intended later use such data. Examples include certain odometer or location coordinate data for a vehicle that may move to and stop at many locations in the course of a day or week, and received signal data that will be analyzed to determine which data, if any, was corrupted by the transmitter and/or by the transmission medium. If these data will be later downloaded from the original memory unit for processing and analysis, it is often crucial that substantially all of these data be received in unaltered form. Preferably, the data to be stored should be receivable in any of several formats and should not require human intervention (e.g., "burning" a CD ROM disk) in order to receive and store a permanent record of these signals.
Many workers have disclosed so-called permanent memory devices which often require human intervention or control in order to provide non-alterability of the data deposited in the memory. Memory devices that express (in binary format) and store odometer data by distinguishing between trip mileage and accumulated mileage for a group of trips and/or that divide a mileage value into two or more mutually exclusive groups of integers representing the greater significance bits and the lesser significance bits are disclosed by Weber in U.S. Pat. No. 4,559,637, by Dubuisson et al in U.S. Pat. No. 4,639,293, by Yamamura et al in U.S. Pat. No. 4,665,497, by Mizuno et al in U.S. Pat. No. 4,682,287, and by Burke et al in U.S. Pat. No. 4,710,888.
However, these patents do not disclose an approach that (1) allows instrument data to be formatted and stored in a modifiable memory in a manner that allows detection of subsequent data alteration, (2) minimizes the number of bits used for representation of a sequence of data values, each drawn from a wide range of values, in a non-modifiable memory, and/or (3) allows each new data value received to be added to the sequence of data values already stored, using the bits representing only the new data value and without requiring change or restatement of any data values that are already stored.